IgM antibodies against Cysticercus cellulosaein the cerebrospinal fluid (CSF) was demonstrated by ELISA immunoenzymatic assay in neurocysticercosis. CSF samples of 41 patients were analyzed for this purpose. Diagnosis was neurocysticercosis in 26 and neurosyphilis in 5; abnormalities were not registered in the other 10 cases. Neurosyphilis samples and no-abnormalities samples were considered as control groups. ELISA IgM assay for cysticercosis was negative in all CSF samples of control groups and it was positive in 12 of the 26 CSF samples of the neurocysticercosis group (46.2%) Titers ranged from 4 till 32. Positive results were no more obtained after previous treatment of CSF samples by 2-mercaptoetanol. ELISA IgM and IgG titers were compared. IgM titers were higher than IgG titers in two cases. Results obtained were compared to those found through complement fixation, immunofluorescence and hemagglutination tests for the diagnosis of neurocysticercosis.